1. Field of the Invention
The present invention generally relates to devices and methods for flow measurement. In particular, a method for continuous multiphase flow measurement is disclosed, as well as the apparatus utilized in the method. In this invention, phase separation and measurement are accomplished utilizing a compact piping arrangement as compared to the measurement vessels utilized in conventional measurement systems.
2. Background
U.S. Pat. No. 5,390,547 (Liu) teaches a multiphase flow measurement method and apparatus using a piping arrangement. U.S. Pat. No. 6,032,539 (Liu et al.) teaches a method and apparatus to automatically calibrate a water cut measurement device to improve the measurement accuracy. These inventions use a two phase measurement technique, in that the incoming multiphase flow stream (i.e., natural gas, crude oil, and produced water) are separated into two separate streams, namely a gas phase and a liquid phase. The gas phase predominantly comprises natural gas. The liquid phase predominantly comprises a mixture of crude oil and produced water. In these devices, no further separation of the liquid phase occurs. Instead, a “water cut meter” is used to determine the water content in the liquid stream. The respective volumes of net oil and produced water are ascertained by applying the water cut measurement to the total liquid flow rate.
However, as the water cut in the liquid stream increases, the net oil measurement loses accuracy because the net oil measurement resolution sharply decreases when the water cut of the production stream increases. An increase in water cut is common for mature, depleting water drive hydrocarbon reservoirs.
U.S. Pat. No. 7,311,001 (also by Liu) provides for separation of the liquid phase components, but this device utilizes a horizontal section having two vertical chambers, where a weir plate divides the first vertical chamber from the second vertical chamber.